SEMANTIC INFORMATION PREPROCESSING FOR NATURALLANGUAGE INTERFACES TO DATABASESbyMilan

A natural language interface to a database (NLID) needs both syntactic information about the structure of language and semantic information about what words and phrases mean with respect to the database. A semantic part of the NLID can implicitly or explicitly provide constraints on the input language. A parser can use these constraints to resolve ambiguities and to decrease overall response time. Our approach is to extract these constraints from the semantic description of the database domain and incorporate them semi-automatically or automatically into information directly accessible to the parser. The advantage of this approach is a greater degree of system modularity, which usually reduces complexity, reduces the number of possible errors in the system and makes it possible to develop di erent parts of the system concurrently by di erent persons and thus reducing development time. Also domain independent syntactic information can be reused from domain to domain, then customized according to the semantic information from a speci c domain. To implement the idea, Abductive Equivalential Translation (AET) was chosen to describe the database related semantics. AET provides a formalism which describes how a \literal" logical form of an input sentence consisting of lexical predicates can be translated to a logical form consisting of predicates meaningful to the database engine. The information used in the translation process is a Linguistic Domain Theory (LDT) based on logic. We shall constrain the expressive power of LDT to suit tractability and e ciency requirements and introduce Restricted Linguistic Domain Theory (RLDT). The main step for incorporation of semantic constraints into the syntax formalism is then extensive preprocessing of the semantic information described by an RLDT into Normalized Linguistic Domain Theory (NLDT). The system uses NLDT to produce selectional restrictions that follow from the semantic description of a domain by RLDT. Selectional restrictions in general iii state which words can be immediately combined with which other words. Once NLDT is constructed, it can be used as a main source of information for semantic processing of a sentence. Thanks to the soundness and completeness of the normalization process, the designer of the interface has possibility to express the semantic knowledge in more declarative terms.